The present invention is generally related to measurements of eyes and systems for measuring ocular surfaces. The invention provides devices, systems, and methods for measurement of hydration and tear volume of an eye in conjunction with measurements of optical errors of the eye and refractive properties of the surfaces of the eye, and is particularly well-suited for diagnosing conditions of the eye in relation to physiologic conditions and refractive properties of the eye. The invention is also particularly well suited to the measurement of eyes in conjunction with diagnosis and correction of optical errors of the eye, including correction with optical surfaces such as lenses, spectacles and contacts.
Known laser eye surgery procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye. The laser typically removes a selected shape of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea's contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of ablation energy across the cornea may be provided by a variety of systems and methods, including the use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue removed being determined by the shape, size, location, and/or number of laser energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to correct a refractive error of the eye. Known systems make use of a variety of forms of lasers and/or laser energy to effect the correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in the cornea, intraocular lenses, removable corneal support structures, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, astigmatism, and the like. However, as with all successes, still further improvements would be desirable. Toward that end, wavefront measurement systems are now available to measure the refractive characteristics of a particular patient's eye. By customizing an ablation pattern based on wavefront measurements and providing improved laser system calibration, it may be possible to correct minor refractive errors so as to reliably and repeatably provide visual accuities greater than 20/20.
Known methods for calculation of a customized ablation pattern using wavefront sensor data generally involves mathematically modeling an optical surface of the eye such as a measured wavefront elevation map and can include corneal topography of the eye. Such work generally assumes that the refractive properties of the eye and surfaces of the eye are stable. Work in connection with the present invention suggests that the known methodology for measuring eyes in relation to refractive surgery and other correction of refractive errors of the eye may be less than ideal.
In light of the above, it would be desirable to provide improved optical measurement techniques, particularly for use in measurements of the eye for refractive correction purposes.